1. Field of the Invention
The present invention relates to a signal processing device, more particularly to processing of character signals with respect to video signals.
2. Description of Related Art
Conventionally, in a camera-integrated VTR (video tape recorder), it has been common practice that a character signal indicating a character, a symbol or the like is superimposed on a video signal captured by a camera or on a reproduced video signal, so as to be displayed on an EVF (Electronic Viewfinder).
FIG. 6 is a block diagram showing the configuration of a circuitry for superimposing such a character signal on a video signal in the above kind of VTR.
In FIG. 6, a superimposition data generating circuit 403 includes a video RAM 409 and a character generator 411, and generates a character signal to be superimposed on a video signal by using the video RAM 409 and the character generator 411.
Storage areas of the video RAM 409 respectively correspond to portions of a display image plane. For example, in a case where the display image plane is divided into twelve areas in the horizontal direction and eight areas in the vertical direction, the divided storage areas of the video RAM 409 become as shown in FIG. 7. A microcomputer 401 writes code data indicative of a character to be displayed, into each storage area 501 of the video RAM 409. The superimposition data generating circuit 403 reads out code data from the video RAM 409 in accordance with a synchronizing signal included in a video signal and inputted from a terminal 405 and outputs the code data to a character generator 411. The character generator 411 generates character signals according to each code data read out from the video RAM 409 and outputs the character signals to combining circuits 413, 419 and 417, from terminals A, B and C, respectively.
The combining circuit 419 combines the character signal outputted from the terminal B of the superimposition data generating circuit 403 with a video signal inputted from a terminal 407 and outputs the thus-obtained composite signal 423 to a processing circuit (not shown) in a recording system as a recording video signal 423. Additionally, the combining circuit 417 combines the output signal 423 of the combining circuit 419 and the character signal outputted from the terminal C of the superimposition data generating circuit 403 and outputs the thus-obtained composite signal 425 to an external apparatus.
An RGB conversion circuit 415 converts the output signal 423 of the combining circuit 419 into RGB signals and outputs the RGB signals to the combining circuit 413. The combining circuit 413 combines the character signal outputted from the terminal A of the superimposition data generating circuit 403 and the RGB signals outputted from the RGB conversion circuit 415 and outputs the thus-obtained composite signal 421 to an EVF (not shown).
As described above, in the conventional circuitry, the video RAM is separated into a plurality of areas corresponding to portions to a display image plane, and a code indicative of a character is written in an area on the video RAM that corresponds to a location in which the character is desired to be displayed.
Accordingly, when the number of characters desired to be displayed is intended to increase, the number of divisions of storage areas of the video RAM is increased to a great number, so that the number of locations in which characters are displayed can be increased.
However, if the video RAM is divided into a great number of areas as described above, an area for displaying one character has to be made small, so that the quality of a displayed character would lower.
On the other hand, if a display area for a character is enlarged to improve the quality of the displayed character, the number of divisions of storage areas 501 of the video RAM has to be decreased, so that locations for displaying characters would decrease.
In addition, as described above, since a character to be superimposed and a display location for the character are determined depending upon an output destination of the video signal, a storage area of the video RAM is also inevitably determined depending upon an output destination of the video signal.
In other words, for example, into an area into which a character code for the EVF is to be written, a character code for another kind of display cannot be written.
For this reason, when it is desired to change a location to display a character depending upon diversities of apparatus models, it is required to redesign the superimposition data generating circuit.
In addition, since the superimposition data generating circuit of such a type has been constructed by using a memory which is different from a memory used in a recording and reproduction circuit, the circuit scale is hindered from being made smaller.